1. Field of the Invention
The present invention relates to magnetic recording and reproducing heads, and magnetic recording and reproducing apparatuses, and more particularly to the magnetic recording head comprising a magnetic core, the magnetic reproducing head comprising a magnetic yoke, a magnetic recording apparatus having the magnetic recording head, and a magnetic reproducing apparatus having the magnetic reproducing head.
2. Discussion of the Background
In a magnetic recording and reproducing apparatus, a magnetic recording medium stores magnetic information as a magnetization direction of magnetic recording bits on the magnetic recording medium. Therefore, each magnetic recording bit of the magnetic recording medium must stably keep magnetization information, and a large magnetization bit is preferable for the stable maintenance of the magnetic information. However, a narrower track width and a shorter bit length in a track length direction of each magnetic recording bit are required for high-density magnetic recording and reproducing technology. Such a small recording bit of the magnetic recording medium tends to have a large demagnetizing field, the recorded magnetization of each recording bit tends to be unstable, and the reproduced signal output tends to decrease.
For reproducing magnetic information recorded on the magnetic recording media, several MagnetoResistance effect (MR) heads have been proposed. The Spin Valve Giant MagnetoResistance effect (SV-GMR) head is one of the MR head and utilizes a mechanism in which the resistance between magnetically uncoupled ferromagnetic layers is observed to vary as the cosine of the angle between the magnetization of the two layers and is independent of the direction of current flow. The SV-GMR head can obtain a higher signal output in reproducing than Anisotropic MagnetoResistance effect (AMR) heads. The SV-GMR is described in U.S. Pat. No. 5,206,590.
Another MR head using a different mechanism termed Tunnel MagnetoResistance effect (TMR) is also reported. The mechanism is obtained by a structure including a ferromagnetic layer, a dielectric tunnel barrier layer, and a ferromagnetic layer and is expected to realize higher reproducing signal output than the SV-GMR head.
Each MR head has a magnetic gap at a surface facing the magnetic recording medium and a shorter magnetic gap length in a track length direction is required to obtain the small magnetic recording bit. However each head has the MR element in the magnetic gap at the medium-facing surface, and that gap must have a marginal minimum length. For example, the SV-GMR and TMR heads need a minimum magnetic gap length of about 100 nanometers. Each MR head having the MR element at the medium-facing surface is called a shield MR head.
A lower flying height between the magnetic head and the magnetic recording medium is also required for high-density magnetic recording and reproducing, and the lower flying height increases frequency of collision between the magnetic head and the magnetic recording medium. The increased number of collisions produces an irregular magnetoresistance, such as Thermal Asperity (TA) noise, of the MR element disposed at the medium-facing surface.
Each of the shield magnetic recording and reproducing heads has the above described marginal minimum gap length as well as the TA noise, and in view of this, a magnetic head using a pair of magnetic yokes has been developed for the shorter magnetic gap length and the reduced TA noise. The pair of magnetic yokes in the magnetic head extends from a medium-facing surface to a region recessed from the medium-facing surface and transfers signal magnetic field from the medium-facing surface to the recessed region where the pair of magnetic yokes are magnetically coupled to a MR element disposed on the recessed region.
The magnetic reproducing head using the pair of magnetic yokes has an advantage that the MR element can be disposed on rear surfaces of the pair of magnetic yokes so the entire body of the MR element is disposed near the medium-facing surface. The rear surfaces of the pair of magnetic yokes are parallel to the medium-facing surface. The magnetic reproducing head having the MR element disposed on the rear surfaces of the pair of magnetic yokes is the so-called horizontal or planar magnetic reproducing head. The planar magnetic head has the pair of magnetic yokes and the MR element. Each of the pair of magnetic yokes extends from the medium-facing surface to the rear surface, which is parallel to the medium-facing surface. The planar magnetic reproducing head is described in U.S. Pat. No. 5,274,521.
The planar magnetic reproducing head is generally manufactured through forming the pair of magnetic yokes on a substrate, forming the MR element on top surfaces of the pair of magnetic yokes, and removing and separating the substrate from the magnetic yoke and the MR element. Surfaces of the pair of magnetic yokes facing the substrate are the medium-facing surfaces, and the top surfaces of the pair of magnetic yokes are the rear surfaces.
The planar magnetic reproducing head tends to have reproducing noise caused by magnetic domain wall generated in the pair of magnetic yokes, and also tends to produce an unexpected magnetic field to the magnetic recording medium caused by residual magnetization in the pair of magnetic yokes. Such reproducing noise is suppressed by a magnetic domain control by providing a bias magnetic field to the pair of magnetic yokes and a conductor layer for producing a magnetic action of a current to the magnetic yoke to suppress the magnetic domain wall in the pair of magnetic yoke. Such magnetic domain control is disclosed in U.S. Pat. No. 5,274,521. In the planar magnetic reproducing head, respective tips of the pair of magnetic yokes for high recording and reproducing density must be as small as about 1 square micrometer or less, and domain control of the small magnetic yoke tips tends to be incomplete.